Re: [PATCH V5 1/4] ACPI: Support Generic Initiator only domains

[Tao Xu]

On 11/13/2019 5:47 PM, Jonathan Cameron wrote:
> On Tue, 12 Nov 2019 09:55:17 -0800
> Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> > [ add Tao Xu ]
> >
> > On Fri, Oct 4, 2019 at 4:45 AM Jonathan Cameron
> > <Jonathan.Cameron@xxxxxxxxxx> wrote:
> > > Generic Initiators are a new ACPI concept that allows for the
> > > description of proximity domains that contain a device which
> > > performs memory access (such as a network card) but neither
> > > host CPU nor Memory.
> > >
> > > This patch has the parsing code and provides the infrastructure
> > > for an architecture to associate these new domains with their
> > > nearest memory processing node.
> >
> > Thanks for this Jonathan. May I ask how this was tested? Tao has been
> > working on qemu support for HMAT [1]. I have not checked if it already
> > supports generic initiator entries, but it would be helpful to include
> > an example of how the kernel sees these configurations in practice.
> >
> > [1]: http://patchwork.ozlabs.org/cover/1096737/
>
> Tested against qemu with SRAT and SLIT table overrides from an
> initrd to actually create the node and give it distances
> (those all turn up correctly in the normal places).  DSDT override
> used to move an emulated network card into the GI numa node.  That
> currently requires the PCI patch referred to in the cover letter.
> On arm64 tested both on qemu and real hardware (overrides on tables
> even for real hardware as I can't persuade our BIOS team to implement
> Generic Initiators until an OS is actually using them.)
>
> Main real requirement is memory allocations then occur from one of
> the nodes at the minimal distance when you are do a devm_ allocation
> from a device assigned. Also need to be able to query the distances
> to allow load balancing etc.  All that works as expected.
>
> It only has a fairly tangential connection to HMAT in that HMAT
> can provide information on GI nodes.  Given HMAT code is quite happy
> with memoryless nodes anyway it should work.  QEMU doesn't currently
> have support to create GI SRAT entries let alone HMAT using them.
>
> Whilst I could look at adding such support to QEMU, it's not
> exactly high priority to emulate something we can test easily
> by overriding the tables before the kernel reads them.
>
> I'll look at how hard it is to build an HMAT tables for my test
> configs based on the ones I used to test your HMAT patches a while
> back.  Should be easy if tedious.
>
> Jonathan
Indeed, HMAT can support Generic Initiator, but as far as I know, QEMU 
only can emulate a node with cpu and memory, or memory-only. Even if we 
assign a node with cpu only, qemu will raise error. Considering 
compatibility, there are lots of work to do for QEMU if we change NUMA 
or SRAT table.